1. Field of the Invention
The present invention relates to an improved electrophotographic photosensitive member, and more particularly, to an electrophotographic photosensitive member employing an azo pigment suitable as a charge-generating material for photosensitive layers comprising a charge generation layer and a charge transport layer.
2. Description of the Prior Art
There have so far been known selenium, cadmium sulfide, zinc oxide, etc. as photoconductive materials for use in electrophotographic photosensitive members. In contrast to many advantages thereof, such as, for instance, chargeability in the dark to a suitable potential, a little dissipation of charge in the dark, and fast dissipation ability by light irradiation, these photoconductive materials have the disadvantages of lacking the film forming property per se with a very few exceptions such as amorphous selenium and of poor ability to retain the charge given to their surface.
On the other hand, a variety of organic photoconductive materials are known, including photoconductive polymers such as polyvinylcarbazole or polyvinylanthracene, which, however, cannot be said so useful in practice since they generally have neither enough sensitivity for actual uses nor a sufficient good film forming property.
In view of the above, a photosensitive member of laminate structure has been recently proposed which comprises two photosensitive layers, a charge generation layer and a charge transport layer, having allotted functions. The electrophotographic photosensitive member having such photosensitive layers of laminate structure has been improved in sensitivity to visible light, in charge retentivity, and in surface strength.
Such a photosensitive member is disclosed in for example, U.S. Pat. Nos. 3,837,851, 3,484,237, and 3,871,882, and U.K. Pat. No. 1453024.
However, electrophotographic photosensitive members still do not have sufficient sensitivity and result in variations in surface potential particularly an increase in light portion potential and a decrease in dark portion potential, upon repeating charge and exposure.